package main

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"encoding/hex"
	"fmt"
	"io"
)

func generateID(prefix string, nBytes int) (string, error) {
	b := make([]byte, nBytes)
	if _, err := io.ReadFull(rand.Reader, b); err != nil {
		return "", err
	}
	return prefix + hex.EncodeToString(b), nil
}

func generateSecret() (string, error) {
	b := make([]byte, 32) // 256-bit
	if _, err := io.ReadFull(rand.Reader, b); err != nil {
		return "", err
	}
	return hex.EncodeToString(b), nil
}

func encryptSecret(plaintext, keyHex string) (string, error) {
	key, err := hex.DecodeString(keyHex)
	if err != nil {
		return "", fmt.Errorf("decode key: %w", err)
	}
	if len(key) != 32 {
		return "", fmt.Errorf("encryption key must be 32 bytes (64 hex chars)")
	}

	block, err := aes.NewCipher(key)
	if err != nil {
		return "", err
	}
	aead, err := cipher.NewGCM(block)
	if err != nil {
		return "", err
	}

	nonce := make([]byte, aead.NonceSize())
	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
		return "", err
	}

	ciphertext := aead.Seal(nonce, nonce, []byte(plaintext), nil)
	return hex.EncodeToString(ciphertext), nil
}

func decryptSecret(ciphertextHex, keyHex string) (string, error) {
	key, err := hex.DecodeString(keyHex)
	if err != nil {
		return "", fmt.Errorf("decode key: %w", err)
	}
	if len(key) != 32 {
		return "", fmt.Errorf("encryption key must be 32 bytes (64 hex chars)")
	}

	ciphertext, err := hex.DecodeString(ciphertextHex)
	if err != nil {
		return "", fmt.Errorf("decode ciphertext: %w", err)
	}

	block, err := aes.NewCipher(key)
	if err != nil {
		return "", err
	}
	aead, err := cipher.NewGCM(block)
	if err != nil {
		return "", err
	}

	nonceSize := aead.NonceSize()
	if len(ciphertext) < nonceSize {
		return "", fmt.Errorf("ciphertext too short")
	}

	nonce, ciphertext := ciphertext[:nonceSize], ciphertext[nonceSize:]
	plaintext, err := aead.Open(nil, nonce, ciphertext, nil)
	if err != nil {
		return "", err
	}
	return string(plaintext), nil
}